The skeletal system includes many long and flat bones which, for example with respect to a human body, extend from the human torso. These bones include the pelvis, spine, humerus, radius, ulna, bones of the hand, femur, tibia, fibula, and bones of the foot. These bones are particularly exposed to trauma from accidents which can cause complex and devastating fractures of the bones. In particular, the femur, tibia, and humerus are often fractured close to the hip joint, knee joint, ankle joint, shoulder joint, and elbow joint. Frequently, the distal and/or proximal portions of the long bone that is fractured must be secured to a bone plate with the major fracture fragments aligned anatomically.
Pins, bone plates and bone screws have been used for repairing fractured bones. The plates are usually placed longitudinally along the periphery of the long bone and have holes or openings through which screws may be inserted into the long bone transversely. When the fracture of a long bone occurs at its end, many bone fragments often result and must be reconnected. The bone plate is ideally placed distal and/or proximal to the fractured area to permit securing of these fragments.
Bone plates that are contoured to the anatomy of a bone have been provided for the fixation of bone fractures and osteotomy fixation. Such bone plates typically either allow for rigid locking of the screw into the plate hole in only one direction or allow the screw to be directed in any plane and then locked. If the plate holes allow for only one direction of insertion, the optimal position of the screw in the plate may not allow for fracture fragment capture by the screw. If the plate holes allow the screw to be directed in a multidirectional manner, screws may capture bone fragments not otherwise captured. Further, currently provided bone plates with multidirectional screw locking mechanisms in the plates do not offer the ability to use the orientation of the screw to align the bone fragments, as may be done with a currently-provided bone plate having a screw fixed or locked in a single direction.
Locking plates have recently been developed for use in spinal and long bone applications. Such plates have bushings that are internally threaded and externally smooth and circular so as to pivot within the bone plate openings and thus allow for multidirectional bone screw insertion. Unfortunately, when locking a bone screw into one of these plates, the pivot movement of the bone screw relative to the bone plate is hindered by the friction of the smooth outer surface of the bushing and the radial force applied by the conical screw head to the internally-threaded surface of the bushing that causes the bushing to expand. The force applied to the screw in the frontal and sagittal planes of the body may cause a loss of stability between the screw head and the plate.
There is a need for a new bone fastening assembly that overcomes the foregoing disadvantages.